Buck regulator with monolithic N- channel upper FET and pilot current sensing

Abstract

A power switching stage architecture for a buck topology-based, DC—DC converter includes an upper power switching N-channel device FET integrated in the same semiconductor circuit chip with the switching driver, while a lower power switching is also an N-channel FET, but is external to the driver chip. Either of the two power switching FETs may be configured to include a pilot FET cell, to facilitate current sensing for the controller.

What is claimed is:  
     
       1. In an apparatus for generating a regulated direct current (DC) output voltage, said apparatus including a buck topology-based, DC—DC converter coupled to a supply voltage, and being operative to generate a regulated output voltage derived from said supply voltage, said DC—DC converter having a pulse width modulation (PWM) generator which generates a PWM switching signal for application to a switching circuit driver, that switchably controls operation of a switching circuit containing upper and lower power switching NFET devices coupled between respective first and second power supply terminals, a common node thereof being coupled through an inductor element to an output voltage terminal, and a controller for controlling the operation of said PWM generator, 
       the improvement wherein  
       said upper power switching NFET device is formed in a common integrated circuit with said switching circuit driver, and said lower power switching NFET device is external to said common integrated circuit.  
     
     
       2. The improvement according to  claim 1 , wherein said upper power switching NFET device includes a pilot NFET cell array that produces a sense current in accordance with current flow through said upper power switching NFET device, said sense current being coupled to said controller for adjusting the duty cycle of said PWM signal to maintain said DC—DC converter's output within a prescribed set of parameters. 
     
     
       3. The improvement according to  claim 1 , wherein said lower power switching NFET device includes a pilot NFET cell array that produces a sense current in accordance with current flow through said lower power switching NFET device, said sense current being coupled to said controller for adjusting the duty cycle of said PWM signal to maintain said DC—DC converter's output within a prescribed set of parameters. 
     
     
       4. A method of configuring a buck topology-based, DC—DC converter that is operative to generate a regulated output voltage derived from a supply voltage, said method comprising the steps of: 
       (a) providing a pulse width modulation (PWM) generator which generates a PWM switching signal for application to a switching circuit driver, that switchably controls operation of a switching circuit containing upper and lower power switching NFET devices coupled between respective first and second power supply terminals, a common node thereof being coupled through an inductor element to an output voltage terminal, and a controller for controlling the operation of said PWM generator;  
       (b) integrating said upper power switching NFET device in a common integrated circuit with said switching circuit driver; and  
       (c) providing said lower power switching NFET device external to said common integrated circuit.  
     
     
       5. The method according to  claim 4 , wherein step (b) comprises configuring said upper power switching NFET device to include a pilot NFET cell array that produces a sense current in accordance with current flow through said upper power switching NFET device, and coupling said sense current to said controller for adjusting the duty cycle of said PWM signal to maintain said DC—DC converter's output within a prescribed set of parameters. 
     
     
       6. The improvement according to  claim 4 , wherein step (c) comprises configuring said lower power switching NFET device to include a pilot NFET cell array that produces a sense current in accordance with current flow through said lower power switching NFET device, and coupling said sense current to said controller for adjusting the duty cycle of said PWM signal to maintain said DC—DC converter's output within a prescribed set of parameters. 
     
     
       7. A DC—DC converter for generating a regulated output voltage derived from a supply voltage, comprising: 
       a pulse width modulation (PWM) generator which generates a PWM switching signal for application to a switching circuit driver, that switchably controls operation of a switching circuit containing upper and lower power switching NFET devices coupled between respective first and second power supply terminals, a common node thereof being coupled through an inductor element to an output voltage terminal; and  
       a controller for controlling the operation of said PWM generator; and wherein  
       said upper power switching NFET device is formed in a common integrated circuit with said switching circuit driver, and said lower power switching NFET device is external to said common integrated circuit.  
     
     
       8. The DC—DC converter according to  claim 7 , wherein said upper power switching NFET device includes a pilot NFET cell array that produces a sense current in accordance with current flow through said upper power switching NFET device, said sense current being coupled to said controller for adjusting the duty cycle of said PWM signal to maintain said DC—DC converter's output within a prescribed set of parameters. 
     
     
       9. The DC—DC converter according to  claim 7 , wherein said lower power switching NFET device includes a pilot NFET cell array that produces a sense current in accordance with current flow through said lower power switching NFET device, said sense current being coupled to said controller for adjusting the duty cycle of said PWM signal to maintain said DC—DC converter's output within a prescribed set of parameters.